The present invention relates to an ink jet recording apparatus and an ink jet recording method using the same. More particularly, the present invention relates to an ink jet recording apparatus and an ink jet recording method using the same, which prevents an increase of a viscosity of the ink in each nozzle of the recording head by vibrating the ink meniscus to such an extent as not to eject an ink drop.
As well known, the ink jet printer is provided with a recording head having a number of nozzles arrayed in a subscanning direction (vertical direction). To print, the recording head is moved in a main scanning direction (horizontal direction) by a carriage mechanism, and a printing medium, e.g., a printing paper, is fed or moved in the subscanning direction. The printer receives print data from a host computer connected thereto, develops the print data into dot pattern data, and drives the recording head, in accordance with the dot pattern data, to eject ink drops through orifices of the nozzles of the recording head at predetermined timings. Those ink drops land on a printing medium, such as a printing paper or an OHP sheet, to print characters, graphical objects and others on the printing medium.
To prevent ink bleeding, it is desirable that the ink drop is quickly dried and solidified. To this end, the ink is generally prepared so that its ink solvent quickly evaporates. It is a rare case that ink drops are ejected through all the nozzle orifices. In most cases, the recording head ejects ink drops toward predetermined or selected positions on the printing medium during a main scanning operation. Accordingly, each main scanning period includes ink ejection periods to eject ink drops and non-ejection periods to eject no ink drops. During the non-ejection period, each nozzle allows water to evaporate from the ink through its orifice, so that a viscosity of the ink increases (referred to frequently as a viscosity increase). The nozzles located at the top and bottom positions on the head face of the recording head are infrequently used when comparing with those nozzles located in the central portion on the head face. Therefore, in the top and bottom nozzles the non-ejection period is long, and those nozzles frequently suffer from the viscosity increase. The viscosity increase brings about many problems: the flying performance of the ejected ink drop is unstable, the nozzle is clogged with dried ink, and the print quality is deteriorated.
To prevent the nozzle clogging, the recording head is usually flushed under predetermined conditions. Specifically, the following operation is periodically performed. The recording head is retracted to a cleaning region, small amounts of ink drops are forcibly discharged from all the nozzles to refresh the ink located near the nozzle orifices.
When the recording head is flushed, the ink near the nozzle orifices is forcibly replaced with fresh ink. In this case, the forcibly discharged ink is wasted, leading to increase of print cost. Further, the flushing operation inevitably interrupts the printing operation. The interruption of the printing operation decreases the printing speed per page, and hence increases of the print time. In recent years, the color printing is widely used. In the circumstances, the nozzles of each color inevitably suffer from the viscosity increase problem.
A technique to refresh the ink near the nozzle orifice by finely vibrating the meniscus of ink during the main scanning operation as well as to forcibly discharge the ink is disclosed in Japanese Patent Publication 57-61576A, for example. To refresh the ink near the nozzle orifice, the technique applies fine pulse signals to the piezoelectric vibrators during the main scanning operation, to thereby finely vibrate the meniscus to such an extent as not to discharge the ink drop. Hereinafter, xe2x80x9cfine vibrationxe2x80x9d means vibration whose amplitude do not eject ink from the nozzle orifices.
As described above, the related technique vibrates the meniscus to prevent the ink viscosity thereof from increasing. However, frequent operations of vibrating the meniscus urges the solvent of the ink to evaporate, possibly resulting in an increase of ink viscosity. Some time elapses till the vibration of the meniscus damps and the vibrating meniscus settles down. If the meniscus is finely vibrated just before an ink drop is ejected, the quantity, shape and a flying path of the ink drop will vary, deteriorating the print quality. The fine vibration influence on a viscosity of ink near the nozzle orifice depends on ambient temperature, aging of the ink and other factors. Application of a uniform fine vibration to the meniscus in circumstances where various related parameters vary from moment to moment will entail an excessive vibration of the meniscus. The excessive vibration leads to increase of the ink viscosity. Thus, it is safe to say that the related technique lacks relationships between the meniscus and the operating conditions of the nozzles (ink drop ejection time and position), ambient conditions and the like, and hence the related technique succeeds in presenting an insufficient solution to the viscosity increase problem.
Accordingly, an object of the present invention is to provide an ink jet recording apparatus and an ink jet recording method using the same which is free from the viscosity increase problem, and stabilizes a flying path of an ink drop ejected, with a unique and novel technical idea that the meniscus of ink in each nozzle is finely vibrated under the control based on the operating conditions of each nozzle.
To achieve the above object, an ink jet recording apparatus of the present invention is arranged such that operating conditions of each nozzle are analyzed in advance, and necessary fine vibration is applied to the meniscus of ink in each nozzle at necessary positions.
In order to achieve the above object, there is provided an ink jet recording apparatus comprising: a recording head provided with nozzles each from which an ink drop is ejected by operating associated pressure generating elements in accordance with inputted print data; driving signal generating means for generating a first driving signal and a second driving signal, the first driving signal for operating the pressure generating element so as to eject the ink drop, the second driving signal for operating the pressure generating element such an extent as to not eject the ink drop; data generating means for selecting at least one predetermined operation pattern for operating the pressure generating element in accordance with operating condition of each nozzle analyzed with reference to the print data in order to generate a dot pattern data in which the first and second data are arranged in accordance with the selected pattern; and switching means for inputting the first and second driving signals to the pressure generating element in accordance with the dot pattern data for each printing period.
The xe2x80x9cpressure generating elementxe2x80x9d is an element capable of varying a pressure of ink in accordance with an input signal applied thereto, and is preferably a piezoelectric element which expands and contracts in accordance with an input signal. A heat generating element, which generates air bubbles when it is heated and varies a pressure of ink by the generated bubbles, may be used for the pressure generating element. The xe2x80x9csecond driving signalxe2x80x9d may be a signal capable of finely vibrating the meniscus of ink to such an extent as to not eject an ink drop through the nozzle. It may take various energy levels and variation forms. The first and second data are typically expressed in terms of xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d. When xe2x80x9c1xe2x80x9d is set to the print bit data (print bit data is made valid), the ink drop is ejected. When xe2x80x9c0xe2x80x9d is set to the first data (first data is made invalid), the ink drop is not ejected. When the second data is valid, a fine vibration is applied to the meniscus of ink (i.e., the meniscus is finely vibrated). When the second data is invalid, a fine vibration is not applied to the meniscus of ink (i.e., the meniscus is not vibrated). The xe2x80x9coperating conditions of each nozzlexe2x80x9d means an ink dot forming state by each nozzle, viz., a printing period where an ink drop is to be ejected.
When receiving print data from a word processor, a personal computer, a work station, a digital still camera or the like, the data generating means analyzes the operating conditions of each nozzle by use of the print data, and selects an operation pattern in accordance with the operating conditions analyzed. One or larger number of operation patterns may be stored. The data generating means sets the second data at predetermined positions in accordance with a selected operation pattern, to thereby generate a dot pattern data. The second data is set to xe2x80x9c1xe2x80x9d during a printing period where a fine vibration is to be applied to the ink meniscus of those printing periods of one main scanning. The second data is set to xe2x80x9c0xe2x80x9d during a printing period where a fine vibration is to not be applied to the ink meniscus.
The thus generated operation pattern data is input to the switching means. When the second data is xe2x80x9c1xe2x80x9d, the switching means allows the first driving signal, which is generated by the driving signal generating means, to go to the pressure generating element. The pressure generating element vibrates at such an amplitude as not to eject an ink drop, and the meniscus of ink in the nozzle associated with the vibrating pressure generating element finely vibrates to refresh ink. When the second data is xe2x80x9c0xe2x80x9d, the switching means prohibits the second driving signal from going to the pressure generating element. When the first data is xe2x80x9c1xe2x80x9d, the switching means allows the first driving signal to go to the pressure generating element to eject an ink drop. When it is xe2x80x9c0xe2x80x9d, the switching means prohibits the first driving signal from going to the pressure generating element.
Therefore, necessary fine vibration is applied to the meniscus of ink in each nozzle when the fine vibration is needed, in accordance with the operating conditions of each nozzle. Therefore, the ink jet recording apparatus prevents an increase of ink viscosity and stabilize a flying path of the ink drop.
In the thus constructed ink jet recording apparatus, the predetermined operation pattern includes a first operation pattern for generating the dot pattern data in which the second data is set so as to select the second driving signal at a predetermined frequency in the printing period except for a predetermined period preceding to a printing period where the first driving signal is selected. In the first operation pattern, when an ink drop is ejected at a position, the fine vibration is not applied to the ink meniscus during the printing periods for a predetermined period immediately before an ink drop is ejected, but the fine vibration is applied to the meniscus during other printing periods than the printing periods. To be more specific, it is assumed now that a total number of printing periods contained in one main scanning period is N, and that the predetermined period consists of three printing periods. When an ink drop is ejected at the n-th printing period, the meniscus is not vibrated during three consecutive printing periods, i.e., the (nxe2x88x921)th to (nxe2x88x923)th printing periods, but it is vibrated at a predetermined frequency during other printing periods than the former periods, viz., the first to (nxe2x88x924)th printing periods, and the n-th period to Nth period. This instance is valid where the first driving signal first appears and the second driving signal then appears during one main scanning period. Where the second driving signal first appears and then the first driving signal appears during one main scanning period, the fine vibration is stopped at a second driving signal present in the same printing period as of a first driving signal selected to eject an ink drop, or the n-th printing period, and the subsequent ones. Therefore, the vibration of the meniscus is damped before the ink ejection, so that a flying path of the ink drop is stabilized. The xe2x80x9cat a predetermined frequencyxe2x80x9d means that the meniscus is vibrated during all the printing periods in which the second driving signal is permitted to be selected (frequency=100%), and that the meniscus may be vibrated every other printing period (frequency=50%).
In the ink jet recording apparatus, the predetermined operation pattern includes a second operation pattern for generating the dot pattern data in which the second data is not set for a first period preceding to a printing period where the first driving signal is selected, and the second data is set so as to select the second driving signal at a predetermined frequency for a second period preceding to the first period.
In the second operation pattern, when an ink drop is ejected at a position, the fine vibration is not applied to the ink meniscus during the printing periods during a first period immediately before an ink drop is ejected, but the fine vibration is applied to the meniscus during a second time period preceding to the first period. This will be described in more detail by using a case where the first period consists of three printing periods, the second period consists of five printing periods, and an ink drop is ejected at the n-th printing period. In this case, no fine vibration is performed during three consecutive printing periods, i.e., the (nxe2x88x921)th to (nxe2x88x923)th printing periods, within the first period. The fine vibration is applied to the meniscus at a predetermined frequency during the five consecutive printing periods, or the (nxe2x88x924)th to (nxe2x88x928)th printing periods. No fine vibration is not applied to the meniscus during the first to (nxe2x88x929)th printing periods, and n-th and latter printing periods. Therefore, there is no chance that the flying path of the ink drop is unstable, and that unnecessary fine vibration is applied to the meniscus.
The first and second period may be set even in an accelerating region where the recording head is acceleratedly moved.
The carriage mechanism drives the recording head at a stand-by position in a region out of a print region to move in an accelerating manner. When the thus moved recording head reaches a print reference position, it moves at a constant speed. Thus, the second data is applied to this region out of the print region. This feature prevents the viscosity increase even when the ink drop is ejected at the first printing period.
The predetermined operation pattern includes a third operation pattern for generating the dot pattern data in which the second data is not set for a first period subsequent to a printing period where the first driving signal is selected, and the second data is set so as to select the second driving signal at a predetermined frequency for a second period subsequent to the first period.
In the third operation pattern, the fine vibration is applied to the meniscus during the second period spaced from the ink ejection by the first period. This will be described in more detail by using a case where the first period consists of three printing periods, the second period consists of five printing periods, and ink ejection is performed at the n-th printing period. In this case, no fine vibration is applied to the meniscus during three consecutive printing periods, or the n-th to (n+2)th printing periods, while the fine vibration is applied at a predetermined frequency to the meniscus during five consecutive printing periods, or the (n+3)th to (n+7)th printing periods. This feature eliminates an unnecessary vibration of the meniscus immediately after the ink drop is ejected and ink is refreshed, and finely vibrates the meniscus to refresh the ink when evaporation of the solve of the refreshed ink will start.
The predetermined operation pattern includes a fourth operation pattern for generating the dot pattern data in which the second data is set so as to periodically select the second driving signal at a predetermined frequency with respect to a nozzle of which no ink drop is ejected within one main scanning.
In the fourth operation pattern, the fine vibration is periodically applied at a predetermined frequency to the meniscus of ink in a nozzle of which no ink drop is ejected within one main scanning. Such a resting nozzle is frequently found in the upper and lower regions of the head face of the recording head. Typically, in the called interlace drive method, the upper nozzle in the upper end processing is likely to rest, and the lower nozzle in the lower end processing is likely to rest. The upper and lower nozzles are frequency positioned in regions out of the print region. Accordingly, it is frequent that those nozzles do not eject ink drops during one main scanning period. Therefore, a viscosity of ink tends to increase at and near the orifices of those nozzles. The fine vibration is periodically applied to those resting nozzles, to prevent the viscosity increase.
At least one of the predetermined frequency and the period of which the second data is set is variably determined according to ambient temperature.
Parameters, e.g., viscosity of ink, varies depending on the ambient temperature. Therefore, the vibrating period and the predetermined frequency depend on ambient temperature. To cope with this, those are adjusted in accordance with ambient temperature. For example, the frequency for fine vibration is reduced where ambient temperature is high. The temperature may directly be detected by use of a temperature sensing element, e.g., a thermister, mounted on a main control board or the recording head. Further, an accumulative operation may also be used to know ambient temperature.
Namely, it may be configured that the longer period is set in accordance with the lower ambient temperature, or the higher frequency is set in accordance with the lower ambient temperature.
At least one of the predetermined frequency and the period of which the second data is set is variably determined according to a viscosity of the ink.
A viscosity of ink contained in an ink cartridge (or ink tank) will increase since the solvent of the ink evaporates out through the container. Usually, the ink cartridge is made of a material permitting water vapor to transmit therethrough, polyethylene, polyacetal or ABS resin. Therefore, with the lapse of time after the cartridge is installed to the printer, the solvent of the ink gradually evaporates and dissipates through the cartridge, and the ink viscosity gradually increases. A viscosity variation may be obtained by estimating empirically a variation of the ink viscosity with time since installation of cartridge. The vibrating period and the frequency are adjusted by use of the estimated viscosity. For example, the time of applying the fine vibration or the frequency may be increased, as the ink viscosity within the cartridge increases.
Namely, it may be configured that the longer period is set in accordance with longer time since installation of an ink cartridge, or the higher frequency is set in accordance with longer time since installation of an ink cartridge.
At least one of the predetermined frequency and the period of which the second data is set is variably determined according to a solid content density of the ink.
The xe2x80x9csolid content densityxe2x80x9d means a density of a coloring material in color ink. Generally, a solid content density of black ink is higher than that of other color inks. Dark or thin color ink of, for example, yellow, light cyan or light magenta, is low in solid content density. When the ink whose solid content density is relatively high is compared with the ink whose solid content density is relatively low, the former increases its viscosity at higher frequency. Accordingly, necessary vibrating period and frequency depends in value on the solid content density of the ink. Those period and frequency may be adjusted by use of the solid content density gathered in advance.
It may be configured that the longer period is set in accordance with the higher solid content density, or the higher frequency is set in accordance with the higher solid content density.
According to the present invention, there is also provided an ink jet recording method for operating a pressure generating element to eject an ink drop from each of nozzles provided in a recording head, comprising the steps of: analyzing an operation condition of each nozzle based on inputted print data; selecting at least one predetermined operation pattern in accordance with the analyzed operation condition; generating a dot pattern data in which a fine-vibration data for operating the pressure generating element such an extent as to not eject the ink drop is set at a predetermined position therein; and inputting the dot pattern data into the pressure generating element.
This ink jet recording method also produces useful effects comparable with those by the ink jet recording apparatus.
According to the present invention, there is also provided a computer-readable recording medium including a computer program for causing an ink jet recording apparatus, which comprises a pressure generating element operated to eject an ink drop from each of nozzles provided in a recording head, to execute the functions of: analyzing an operation condition of each nozzle based on inputted print data; selecting at least one predetermined operation pattern in accordance with the analyzed operation condition; generating a dot pattern data in which a fine-vibration data for operating the pressure generating element such an extent as to not eject the ink drop is set at a predetermined position therein; and inputting the dot pattern data into the pressure generating element.
The xe2x80x9crecording mediumxe2x80x9d may be any of various semiconductor memory, e.g., ROM or RAM, a floppy disc, a hard disc, a magneto-optical disc, a magnetic tape, an IC card, and the like. Alternatively, communication mean may be used. In this case, necessary programs are down-loaded from a remote location by way of a communication line.
A computer of the ink jet recording apparatus reads a given program from the recording medium; analyzes operating conditions of each nozzle by use of print data; selects a proper operation pattern in accordance with the analysis result; and generates operation pattern data of which the second data is configured according to the selected operation pattern. Therefore, necessary fine vibration may be applied to the meniscus of ink at necessary time points in accordance with the operating conditions, thereby preventing the viscosity increase and stabilizing the flying path of the ink drop.